1. Field of the Invention
The present invention relates to a high-frequency switch module arranged to switch among various high-frequency signals to be transmitted or received.
2. Description of the Related Art
Various high-frequency switch modules for transmitting/receiving a plurality of communication signals in different frequency bands with a single antenna have been recently developed. In such a high-frequency switch module, an SPnT (n represents a positive number) switch IC is generally used. The SPnT switch IC includes an antenna connection port connected to an antenna and a plurality of high-frequency signal input/output ports (including a transmission port, a reception port, and a transmission/reception port.) Switching among the high-frequency signal input/output ports to be connected to the antenna connection port is performed in accordance with a control signal.
In high-frequency switch modules in the related art, a matching circuit for performing impedance matching between a switch IC and an antenna is connected to an antenna connection port of the switch IC. For example, in a high-frequency switch module disclosed in Japanese Unexamined Patent Application Publication No. 2005-505186, a π-type band-pass filter is connected between an antenna connection port and an antenna.
This π-type band-pass filter includes an LC series resonance circuit connected between the antenna connection port of a switch IC and the antenna and two LC parallel resonance circuits for connecting both ends of the LC series resonance circuit to the ground. Furthermore, a capacitor connected in series to the LC series resonance circuit is disposed on the sides of the antenna connection port and the antenna.
The π-type band-pass filter functions not only as an impedance matching circuit but also as an electrostatic discharge (ESD) protection circuit.
A switch IC in such a high-frequency switch module includes an FET and a capacitor. At the time of energization, an electric charge is stored in the FET and the capacitor. When switching control is performed in this state, the switching control is not completed until the stored electric charge is discharged. That is, high-speed discharging is required for high-speed switching.
However, since the capacitor is directly connected to the antenna connection port in the above-described high-frequency switch modules in the related art, it is difficult for an electric charge stored in the switch IC to discharge and a discharge time is increased. This leads to the reduction in a switching speed.